1. Field of the Invention
The present invention relates to waste vitrification processes. More particularly, the present invention relates to a process for stabilizing organics-containing wastes, and to a waste glass product made according to the process. The invention also relates to a process for recovering metals from organics-containing wastes. 2. Discussion of Background
Numerous methods are available for the proper and safe disposal of waste materials, including disposal in landfills, incineration, vitrification, etc. Waste treatment processes may themselves generate hazardous wastes. For example, when solids are filtered from a waste stream, the spent filter medium may contain heavy metals and other hazardous substances, and must be treated and stabilized before disposal. (As used herein, the term "hazardous waste" includes wastes containing substances commonly recognized as hazardous, including but not limited to chemical wastes, radioactive wastes, mixed chemical and radioactive wastes, heavy-metal-containing wastes, and hazardous organics.) Despite these efforts, there remains a large volume of hazardous waste material, including organics-containing waste, that must be safely disposed of.
Many types of wastes, including ion exchange resins and waste electronic components such as used circuit boards, vacuum tubes, transistors and so forth, contain metals, organic compounds and potentially leachable constituents. Even though the concentration of metals in these types of wastes may be small, the overall waste volume is large. In the U.S. alone, these wastes may contain many thousands of pounds of precious metals (Au, Ag, Pt, etc.) as well as base metals (Cu, Pb, Fe, Mn, etc.). There is a growing interest in the recovery of useful metals from these types of wastes.
A number of techniques have been used to treat hazardous waste, including vitrification, which involves dissolving or encapsulating the wastes in a stable, leach-resistant glass matrix. Typically, the waste is mixed or slurried with glass formers and fed to a glass melter, where the mixture is heated until it is molten. The waste is incorporated into the glass matrix in such a way that the final, cooled product resists leaching for very long periods of time. Because glass is very stable against chemical attack, vitrification has been studied for decades in connection with radioactive wastes. Other hazardous wastes and mixed wastes (wastes that contain both radioactive and hazardous materials) may also be treated by vitrification.
However, there are a number of problems associated with vitrification. For example, the quality of the waste glass produced depends on the constituents of the melt, including the composition of the waste itself and the composition of any additives that are added to the waste to form a glass-forming mixture. Stable glass formulations typically contain no organic materials (or only trace amounts of organics), and generally avoid or restrict the concentration of transition metals. Thus, vitrification alone is not suitable for treating wastes that contain substantial amounts of organics and/or transition metals (including precious metals such as Au, Ag, Pd and Pt). These constituents must be recovered or destroyed before the waste residue can be vitrified to form a stable, environmentally safe product.
Catalysts are substances that alter the rate of a process, and are either incorporated into the process without adverse consequences, or recoverable essentially unaltered in form and amount at the end of the process. Many types of catalysts are known, including pure metals such as Fe, Ni and Pt, organic and inorganic compounds, organometallic compounds, and complexes of organic groups and metal halides. The action of a catalyst can be altered by the addition of a catalyst poison, which interferes with catalytic action, or a catalyst promoter, which activates fresh catalysts, reactivates spent catalysts, or reacts with a catalyst poison. Many present-day industrial processes, including waste treatment processes, depend on the use of catalysts.
Catalysts are used in several wastewater treatment processes. Mitsui, et al. (U.S. Pat. No. 4,751,005) use a composite metal oxide catalyst in a process for wet oxidation of wastewater. In U.S. Pat. No. 5,192,452, they also teach contacting water with ozone in the presence of a first catalyst (silicon dioxide, titanium oxide, zirconium oxide or aluminum oxide), then a second catalyst (manganese, iron, nickel, gold, platinum). Lichtin, et al. (U.S. Pat. No. 4,861,484) use transition elements and peroxide (H.sub.2 O.sub.2) for the controlled photodegradation of organic wastes. The wastes, in fluid form, are mixed with the catalyst, then exposed to photoenergy which is absorbed by the catalyst to degrade the wastes. Ishii, et al. (U.S. Pat. No. 5,145,587) disclose wet oxidizing of organics-containing wastewater in the presence of titanium dioxide, an oxide of an element of the lanthanide series, and a metal (Mn, Fe, Cu, Ag, Au, Pt, Pd, etc.) or a water-insoluble or sparingly water-soluble compound of said metal. Also, Wilms, et al. (U.S. Pat. No. 4,294,703) describe a process for treating organic wastes at a temperature in the range 5.degree.-100.degree. C. in the presence of peroxide and a transition metal oxide.
Although many waste treatment processes are known, there is no known, routinely-used, cost-effective process for selectively recovering metals from organics-containing wastes, oxidizing organics contained in the wastes, and stabilizing the waste residue for disposal. Such a process should be simple, flexible, substantially reduce the overall waste volume, and produce a stable, durable product.